Slender-body theory for the generation of micrometre-sized emulsions through tip streaming

Castro-Hernández, Elena; Campo-Cortés, F.; Gordillo, José Manuel

doi:10.1017/jfm.2012.100

Cited by 36 publications

(22 citation statements)

References 30 publications

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“…If the viscous stresses overcome the interfacial tension, the perturbation grows into a fluid filament. This is the tip-streaming phenomenon commonly observed in the microfluidic co-flow geometry [8][9][10]. If instead of a point, the flow is converging to a stagnation line, then a thin sheet can be entrained [11].…”

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confidence: 95%

Streaming from the Equator of a Drop in an External Electric Field

Brosseau

Vlahovska

2017

Phys. Rev. Lett.

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Tip-streaming generates micron-and submicron-sized droplets when a thin thread pulled from the pointy end of a drop disintegrates. Here, we report streaming from the equator of a drop placed in a uniform electric field. The instability generates concentric fluid rings encircling the drop, which break up to form an array of microdroplets in the equatorial plane. We show that the streaming results from an interfacial instability at the stagnation line of the electrohydrodynamic flow, which creates a sharp rim. The flow draws from the rim a thin sheet which destabilizes and sheds fluid cylinders. This streaming phenomenon provides a new route for generating monodisperse microemulsions.A highly conducting drop in a uniform electric field elongates into a prolate ellipsoid whose poles in strong fields deform into conical tips (Taylor cones) emitting jets of charged tiny droplets [1][2][3][4][5]. This so called electrohydrodynamic (EHD) streaming or cone-jetting occurs in many natural phenomena (e.g., drops in thunderclouds) and technological applications (printing, electrospraying, electrospinning) [4,6].The streaming is related to a generic interfacial instability due to a convergent flow [7], see Figure 1.a. The interface is compressed and a local perturbation at the stagnation point (e.g., drop tips) gets drawn by the flow. If the viscous stresses overcome the interfacial tension, the perturbation grows into a fluid filament. This is the tip-streaming phenomenon commonly observed in the microfluidic co-flow geometry [8][9][10]. If instead of a point, the flow is converging to a stagnation line, then a thin sheet can be entrained [11]. By analogy with the cone-jet geometry resulting from the destabilization of a stagnation point, it is expected that the instability of a stagnation line would give rise to an edge-sheet structure. In this Letter, we report for the first time streaming resulting from a stagnation line instability.Experimentally, we exploit the electrohydrodynamic flow about a neutral drop placed in a uniform electric field [12,13]. By varying the fluid conductivities, we are able create flow converging either at the drop poles (Figure 1.b) to generate cone-jet, or at the equator ( Figure 1.c) to generate an edge-sheet. The latter case is the focus of this work. The electrohydrodynamic flow is driven by electric shear stresses due to induced surface charges [12,13]. For a drop in a uniform electric field the resulting flow is axisymmetrically aligned with the applied field. For a spherical drop with radius a placed in DC electric field E = Eẑ, the surface velocity is [12]where λ = µ in /µ ex is the viscosity ratio between the drop and suspending fluids and θ is the angle with the applied field direction. The direction of the surface flow depends on the difference of conductivity, σ, and permittivity, ε, of the drop and suspending fluids R = σ in /σ ex and S = ε in /ε ex . For highly conducting drops, R/S > 1, the surface flow is from the equator to the poles. Accordingly, the poles become stagnation p...

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confidence: 95%

Streaming from the Equator of a Drop in an External Electric Field

Brosseau

Vlahovska

2017

Phys. Rev. Lett.

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“…We have performed further experiments with the goal of recovering an incipient jet for zero voltage. To this end, we have followed the observations by Castro-Hernández et al (2012) for a coflow configuration, where droplets of constant diameter emanate from a jet whose length is reduced by decreasing the inner and outer flow rates but keeping a constant ratio between them. In our current flow focusing geometry, we have reduced the flow rates to Q i = 12.5 µl/h and Q o = 100 µl/h, obtaining jets of the same diameter but shorter.…”

Section: Resultsmentioning

confidence: 99%

Controllable production of Janus ligaments by AC fields in a flow-focusing junction

Castro-Hernández

García-Sánchez

Rodríguez

et al. 2019

Microfluid Nanofluid

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We report the production of bicomponent Janus filaments of miscible aqueous fluids in a microfluidic electro-flow focusing device under the action of an AC electric field. The production of liquid filaments can lead to the generation of microfibers by adding a subsequent process of polymerization. Janus microfibers are of paramount importance in biomedical applications such as tissue production on crimped scaffolds. We show that the filament length is a function of the frequency signal, voltage amplitude and of the viscosity and conductivity of the dispersed phase. In particular, Janus filaments with diameters ∼ 10 µm and longer than 1 mm are produced by AC voltages with frequencies below 150 kHz and a viscosity of the dispersed phase ∼ 10 cP.

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“…Droplet production from a highly focused jet, also known as tip streaming, is a flow mode in which a thin jet emerges from a nearly conical point [23][24][25][26]. The jet is subject to the Rayleigh-Plateau instability [27], and decays into droplets further downstream, whose sizes are set by the radius of the jet.…”

Section: Introductionmentioning

confidence: 99%

“…By contrast, drop formation from the jet occurs by a "convective instability", which grows in a frame of reference convected with the flow. Numerical calculations in simple flow geometries have confirmed the possibility of creating thin jets from the tip of conical points [24,25]. However, jet radii have not been reported in a systematic fashion; in particular, the crucial question of what limits the size of the smallest jet has not been addressed.…”

Section: Introductionmentioning

confidence: 99%

Opposed flow focusing: evidence of a second order jetting transition

et al. 2018

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We propose a novel microfluidic "opposed-flow" geometry in which the continuous fluid phase is fed into a junction in a direction opposite the dispersed phase. This pulls out the dispersed phase into a micron-sized jet, which decays into micron-sized droplets. As the driving pressure is tuned to a critical value, the jet radius vanishes as a power law down to sizes below 1 µm. By contrast, the conventional "coflowing" junction leads to a first order jetting transition, in which the jet disappears at a finite radius of several µm, to give way to a "dripping" state, resulting in much larger droplets. We demonstrate the effectiveness of our method by producing the first microfluidic silicone oil emulsions with a sub micron particle radius, and utilize these droplets to produce colloidal clusters.

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Slender-body theory for the generation of micrometre-sized emulsions through tip streaming

Cited by 36 publications

References 30 publications

Streaming from the Equator of a Drop in an External Electric Field

Streaming from the Equator of a Drop in an External Electric Field

Controllable production of Janus ligaments by AC fields in a flow-focusing junction

Opposed flow focusing: evidence of a second order jetting transition

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